Over the past decade, as telephone users demand more and more capabilities from telephone equipment, various forms of wireless telephone systems have become available. For example, wireless home systems are now available in which a low power base station directly connects to the public switched telephone network ("PSTN") in place of a standard telephone set and provides limited area wireless capability within a home. In addition, cellular mobile telephone use, widely introduced about ten years ago, continues its rapid growth and, in most large metropolitan areas, the 800-900 MHz spectrum assigned to the CMTS has become exceedingly crowded.
The notion of "personal" communications, by which one is always able to reach an individual regardless of his or her location, has become a popular goal of telecommunications companies, and various multi-functional systems have been developed with that objective in mind. For example, U.S. Pat. No. 4,989,230 describes a telephone which has two separate transceivers for accessing the separate frequency bands used by either a wireless home telephone system or a CMTS. U.S. Pat. No. 4,790,000 describes a private wireless system which shares the same frequency band as a CMTS by fixedly preselecting for use by the private wireless system those channels of the CMTS which will not interfere with the CMTS in the local area serviced by the private system.
In the PCS further described below and in the related patent applications whose disclosures are incorporated herein by reference, the PCS continually scans all CMTS voice channels and dynamically selects and maintains a pool of those CMTS voice channels which are idle within the local area serviced by the PCS. These idle channels are made available to the WTS for use as control or voice channels of the WTS.
A number of unique problems arise in implementing the functionalities desired for the PCS handset as it moves around within the WTS as a result of its sharing the same frequency spectrum used by the CMTS and other WTS systems which may be operating in the same local area.
For example, as a consequence of the dynamic scanning and channel allocation process, the WTS control channels may, in principle, be any of the more than 400 channels which are available as CMTS voice channels (on either the A or B side of the cellular spectrum). When the PCS handset attempts to enter the WTS operating mode, it must perform a channel scan to find the appropriate control channel of a WTS in which it may register. However, always scanning all potential WTS control channels is not feasible since the scan time would be inordinately long and paging signals to the PCS handset that occur during the scanning process, indicative of an incoming call, would be missed by the PCS handset, resulting in an unacceptable level of lost incoming phone calls. Accordingly, it is necessary for the PCS handset to implement a scanning procedure which efficiently finds the accessible WTS control channels in a sufficiently short time so as not to lose incoming paging signals.
Further, since there might be many overlapping microcells corresponding to other WTS systems which might be operating within the same locality, once the PCS handset has located the control channel of the WTS system to which it is permitted access, it is desirous that the PCS handset remain tuned to that WTS system even if an adjacent WTS control channel of greater signal strength originating from a different WTS system is received by the PCS handset. In the invention disclosed herein, the scanning procedure implemented by the PCS handset provides this and other capabilities.